Electrical submersible motor

ABSTRACT

A fluid system for a pump, which includes a downhole rotating shaft and bearings inside a housing, and where a fluid volume around shaft is circulated from outside housing through a filter, so that only clean non-abrasive fluid is permitted inside fluid volume pump to draw fluid around the shaft. A fluid expeller is included to expel fluid from the accumulated volume of fluid through the filter to purge the filter.

FIELD OF THE INVENTION

The invention relates to a fluid filter to extend the protector life oreliminate protector of a canned electrical submersible motor.

BACKGROUND OF THE INVENTION

In a variety of wellbore environments, electric submersible pumpingsystems are used to lift fluids from a subterranean location. Althoughelectric submersible pumping systems can utilize a wide variety ofcomponents, examples of basic components comprise a submersible pump, asubmersible motor and a motor protector. The submersible motor powersthe submersible pump, and the motor protector seals the submersiblemotor from well fluid.

The motor protector also balances the internal motor oil pressure withexternal pressure. Motor protectors often are designed with a labyrinthsystem and/or an elastomeric bag system. The labyrinth system uses thedifference in specific gravity between the well fluid and internal motoroil to maintain separation between the fluids. The elastomeric bagsystem relies on an elastomeric bag to physically isolate the motor oilfrom the well fluid while balancing internal and external pressures.Additionally, motor protectors often have an internal shaft thattransmits power from the submersible motor to the submersible pump. Theshaft is mounted in journal bearings positioned in the motor protector.

Such protectors function well in many environments. However, in abrasiveenvironments, the run life of the motor protector can be detrimentallyaffected. The abrasive sand causes wear in motor protector components,such as the journal bearings. Attempts have been made to increase runlife by populating the motor protector with journal bearings made fromextremely hard materials to reduce wear caused by the abrasive sand.

In general, the present invention relates to a motor protector for usein an electric submersible pumping system, or potentially theelimination of the protector in the event of a “canned” motor.

For non-canned motors, the protector is designed to seal a submersiblemotor from well fluid and to keep the motor oil pressure generallybalanced with external pressure.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a means forpreventing sand/solids from entering the motor rotor cavity.

According to further aspect of the invention, there is provided a meansfor preventing sand/solids from entering the motor protector rotorcavity.

According to a further aspect of the invention, the outer most bearingis continuously flushed with filtered well bore fluid.

According to further aspect of the invention, the motor rotor cavity ispressure balanced by a filter medium which allows fluid to both enterand leave the rotor cavity but no solids can enter the rotor cavity.

According to a further aspect of the invention positive fluid flow ispromoted at the use of a flow energising device.

According to a further aspect of the invention any sand/solid isdeflected away from the top of the protector or output shaft from themotor.

According to a further aspect of the invention the rotor cavity willoperate with filtered wellbore fluids.

According to a further aspect of the invention, the rotor cavity willmatch the pressure outside of the motor instantaneously as the filtermedium provides direct communication between the two.

According to a further aspect of the invention, the pump bearings willbe lubricated with filtered fluid.

According to a further aspect of the invention the filter is backflushed.

This invention protects the outer seal and bearing of the protector bycirculating clean filtered fluid from the inside to the outside.

This invention for canned motors ensures only clean filtered fluid canenter the rotor cavity.

Clean filtered fluid in the rotor cavity ensures long run life.

Canned motor ensures motor windings do not fail because of protectorfailure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevation view of an electric submersible pumpingsystem disclosed in a wellbore, according to an embodiment of thepresent invention;

FIG. 2 is a longitudinal sectional view taken generally along an axis ofa motor protector illustrated in FIG. 1

FIG. 3 is a longitudinal section side view of the flow promotion devicefitted between the protector and pump inlet.

FIG. 4 is a more detailed section side view of the flow promotion deviceshown in FIG. 3.

FIG. 5 is a longitudinal section side view of a canned motor with thefilter inlet/outlets fitted at its upper and lower ends.

FIG. 6 is a more detailed section side view of output end of the motorshown in FIG. 5.

FIG. 7 is a more detailed section side view of the lower end of themotor shown in FIG. 5.

FIG. 8 is a similar view to FIG. 3 with the pump section above the flowpromotion device highlighted.

FIG. 9 is a more detailed section side view of the part highlighted inFIG. 8.

FIG. 10 is a section side view of the back flush mechanism

FIG. 11 is a similar view to FIG. 9, with the back flush in operation

FIG. 12 is a more detailed of the back flush mechanism shown in the viewindicated of FIG. 11

In the following description, numerous details are set forth to providean understanding of the present invention. However, it will beunderstood by those of ordinary skill in the art that the presentinvention may be practiced

without these details and that numerous variations or modifications fromthe described embodiments may be possible.

The present invention generally relates to a system and method forreducing detrimental effects of sand on motor protectors. The system andmethod are useful with, for example, a variety of downhole productionsystems, such

as electric submersible pumping systems. However, the devices andmethods of the present invention are not limited to use in the specificapplications that are described herein.

Referring generally to FIG. 1, an example of a pumping system 10, suchas an electric submersible pumping system, is illustrated according toan embodiment of the present invention. Pumping system 10 may comprise avariety of components depending on the particular application orenvironment in which it is used. In this example, however, pumpingsystem 10 includes a submersible pump 12, a submersible motor 14 and amotor protector 16.

Pumping system 10 is designed for deployment in a well 18 within ageological formation 20 containing desirable production fluids, such aswater or petroleum. A wellbore 22 typically is drilled and lined with awellbore casing 24. Wellbore casing 24 includes a plurality of openingsor perforations 26 through which production fluids flow from formation20 into wellbore 22.

Pumping system 10 is deployed in wellbore 22 by a deployment system 28that may have a variety of forms and configurations. For example,deployment system 28 may comprise tubing, such as coil tubing orproduction tubing, connected to pump 12 by a connector 32. Power isprovided to submersible motor 14 via a power cable 34. Motor 14, inturn, powers pump 12 which draws production fluid in through a pumpintake 36, and pumps the production fluid to the surface via tubing 30.

It should be noted that the illustrated submersible pumping system 10 ismerely an example. Other components can be added to this system andother deployment systems may be implemented. Additionally, theproduction fluids may be pumped to the surface through tubing 30 orthrough the annulus formed between deployment system 28 and wellborecasing 24. In any of the many potential configurations of submersiblepumping system 10, motor protector 16 is used to seal the submersiblemotor 14 from well fluid in wellbore 22 and to generally balance theinternal pressure within submersible motor 14 with the external pressurein wellbore 22.

Referring generally to FIG. 2, an embodiment of motor protector 16 isillustrated in greater detail. Motor protector 16 comprises an outerhousing 38 within which a drive shaft 40 is rotatably mounted via aplurality of bearings 42, such as journal bearings. Outer housing 38 maybe formed of one or more housing components. Also, the motor protector16 is divided into a plurality of sections, including a head section 44disposed generally at an upper end of the protector. An additionalsection (or sections) is disposed below head section 44 and functions asa fluid separation section to separate wellbore fluid that may enterhead section 44 from internal motor oil used to lubricate submersiblemotor 14. The sections also facilitate balancing of internal andexternal pressures. In the embodiment illustrated, a labyrinth section46 is disposed below head section 44, and a pair of elastomeric bagsections 48 are disposed below labyrinth section 46.

Labyrinth section 46 comprises a labyrinth 50 that uses the differencein specific gravity of the well fluid and the internal motor oil tomaintain separation between the internal motor oil and the well fluid.Each bag section uses an elastomeric bag 52 to physically isolate theinternal motor oil from the well fluid. It should be noted that themotor protector sections may comprise a variety of section types. Forexample, the motor protector may comprise one or more labyrinthsections, one or more elastomeric bag sections, combinations oflabyrinth and bag sections as well as other separation systems. A seriesof fluid ports or channels 54 connect each section with the nextsequential section. In the embodiment illustrated, a port 54 is disposedbetween head section 44 and labyrinth section 46, between labyrinthsection 46 and the next sequential bag section 48, between bag sections48 and between the final bag section 48 and a lower end 56 of motorprotector 16.

Motor protector 16 may comprise a variety of additional features. Forexample, a thrust bearing 58 may be deployed proximate lower end 56 toabsorb axial loads placed on shaft 40 by the pumping action ofsubmersible pump 12. The protector also may comprise an outward reliefmechanism 60, such as an outward relief valve. The outward relief valvereleases excessive internal pressure that may build up during, forexample, the heating cycle that occurs with start-up of electricsubmersible pumping system 10. Motor protector 16 also may comprise aninward relief mechanism 62, such as an inward relief valve. The inwardrelief valve relieves excessive negative pressure within the motorprotector. For example, a variety of situations, such as system cooldown, can create substantial internal pressure drops, i.e. negativepressure, within the motor protector. Inward relief mechanism 62alleviates the excessive negative pressure by, for example, releasingexternal fluid into the motor protector to reduce or avoid mechanicaldamage to the system caused by this excessive negative pressure.

Referring to FIGS. 3 and 4 there is shown the output shaft from theprotector 100 passing through the assembly 101, the shaft 100 issupported in bearings 102 and 103, and drives the pump via splinedoutput 104 via coupling 105. The pump inlet is shown as passages 106. Inthe event the pump is stopped and sand particles fall out of suspension,they will contact the deflector 107 mounted on the shaft, fall on thesloping surface 108 and fall into the annulus around the pump.

When the shaft 100 is rotating, fluid is drawn through ports 109 througha filter medium 110 into a gallery 111 and pressurized by a screw typepump mechanism 112 back through the bearing 103 and underneath thedeflector 113. This ensures only clean fluid without any damaging solidparticles in it is above the protector, maximising the protector's life.In addition, because the bearing 103 will not deteriorate due toerosion, no additional vibrations will be generated.

Referring to FIGS. 5 to 7, there is shown a canned motor assembly. Thisis where the stator 120 is physically isolated from the rotor cavity 122by a tube 124. This is particularly advantageous with this invention, asthe protector can be eliminated. At the output end above the thrustbearing assembly 114 is an identical mechanism 125 described in relationto FIG. 4. At the motors lower end, the rotor cavity 115 is equalisedwith the fluid around the outside of the motor via a filter medium 117and ports 118 and 119. The filter medium can be selected to filter anyparticle size and have sufficiently volume to have a predicable longlife. The filter medium could be made of different layers with differentfiltering capabilities. The bearing inside the rotor cavity should becapable of running in either oil or water and made from a suitablematerial such as tungsten carbide.

Referring to FIGS. 8 and 9, the flow outlet from the pressuring pump 112exits from below the flow outlet protector 107 via a narrower channel130, and also exits via port 131 into a centre bore of the pump driveshaft 132. At the coupling 133 there are o-rings 134 and 135 which sealon respective shafts 136 and 137, so the pressurised filtered fluid ispumped into a centre bore of the pump shaft 138. Some of the fluid exitsthe bore of pump shaft 138 through a port 139. At pump bearings 141 apassage 140 allows filtered fluid to lubricate the pump bearing 141before passing into the discharge fluid. Several bearings 141 havingsuch passages 140 are distributed along the entire pump shaft length.This feature ensures a long bearing life, and a long endurance of thepump especially in a production fluid with sand other solid particles.

This feature could also be used to supply clear fluids to drillingassembly bearings, and other systems exposed to abrasive fluids.

Referring to FIGS. 10 to 12, there is shown a back flushing mechanism220. Referring particularly to FIG. 12, on the main shaft 100 a cam 200reciprocates a piston 201 in a piston bore 202, clean fluid is fed intothe piston bore 202 via passage 203, on each stroke of the piston 201 asmall volume of fluid is displaced past the check valve 204 into thechamber 205. The annular piston 206 is displaced downwards againstspring 207. A rod 208 attached to the piston unseats a valve 209 so thatthe collet fingers 216 and pushed out of recess 217 which allows thefluid accumulated in the chamber 210 to back flush the filter viapassage 211 and check valve 212. After the spring 207 displaces thepiston fully back to the wall 213, it resets the valve 209. The checkvalve 212, is returned to non-active position by spring member 214,fluid can the pass by the valve 212 into passage 215 to be circulatedwhere required. The charging operation of the back flush mechanism isthen repeated. Typical cycle time for the back flush mechanism will be6-12 hours so the filter will have regular back flushes. This could bechanged depending upon the fluid type being filtered.

In general, any suitable type of pump may be used in conjunction withthis cleaned fluid arrangement; the rotor shaft may include anadditional pumping means, even a simple feature formed on the rotorshaft which tends to induce a fluid flow.

1. A fluid system for a pump, which includes: a downhole rotating shaft and bearings inside a housing, a fluid volume around the shaft, a circulating fluid from outside the housing through a filter, such that only clean non-abrasive fluid is permitted inside fluid volume pump to draw fluid around the shaft.
 2. A fluid system according to claim 1, further including a fluid expeller to expel fluid from the accumulated volume of fluid through the filter to purge the filter.
 3. A fluid system according to claim 1, further including a fluid passage through a bearing or bearings.
 4. A fluid system according to claim 1, further including a protector hood to deflecting falling solids coming out of suspension.
 5. A fluid system according to claim 1, further including a bore through the shaft.
 6. A fluid system according to claim 1, further including a valve and inlet port a piston and a valve and outlet port to backflush the system.
 7. A fluid system according to claim 6, further including a cam on the shaft to drive the fluid through the inlet valve.
 8. A fluid system according to claim 1, wherein two such systems are included at each end of a rotor.
 9. A fluid system according to claim 1, wherein there is a continuous fluid flow through rotor 